Radar modulator control circuit



Oct. 27. 1959 M. P. slEDBAND RADAR MODULATOR CONTROL CIRCUIT Filed March 7, 1956 ATTORNEYS Unite States arent RADAR MODULTOR CONTROL CIRCUIT Melvin P. Siedband, Baltimore, Md., assigner, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application March 7, 1956, Serial No. 570,195

8 Claims. (Cl. 331-88) The present invention relates to a radar modulator control circuit.

A radar modulator, by controlling the operation of a magnetron transmitter tube, causes radio-frequency energy to be produced in short, powerful pulses. The modulator controls the shape, duration, and repetition frequency of the pulses. Usually it exercises control by applying pulses of plate-to-cathode voltage to the magnetron. It is desirable to have constant `magnetron output in radar applications and since the modulator controis the magnetron it is evident that by means of suitable control of the modulator, constant magnetron output` can be obtained. A magnetron may be considered essentially a constant voltage -device with the output radio frequency power directly proportional to the average cathode current for a constant duty cycle and pulse width. The end result of the radar transmitter consists of a train of uniform radio frequency bursts of energy, and deviations from this uniformity manifest themselves as changes in average cathode current of the magnetron. The present invention relates to a circuit for amplifying the cathode current and utilizing this current to bias the radar modulator in a manner such that a closed-loop degenerative system is obtained and thus a control signal that is a function of changes in cathode current is fedv back to cancel the changes. A specific embodiment is shown wherein the bias winding of a saturable core discharge reactor of a magnetic modulator is used to maintain constant magnetron output. Thus, a circuit is disclosed for obtaining constant magnetron output despite line variations, temperature variations, magnetron condition or other factors.

Accordingly, an object of the present invention is the provision of a circuit for controlling magnetron output.

Another object is to provide a circuit for controlling a radar modulator in a manner such that constant radio frequency magnetron output is obtained.

A further object of the invention is the provision of a circuit for biasing a radar modulator such that constant magnetron radio frequency output is obtained.

Still another object is to provide a circuit that utilizes the cathode current of a magnetron to bias a modulator for the magnetron in a manner such that the radio frequency output of the magnetron is maintained essentially constant.

A still further object of the present invention is the provision of a circuit that utilizes the cathode current of a magnetron to bias a winding in a magnetic modulator for the magnetron such that the radio frequency output of the magnetron is maintained essentially constant.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Fig. 1 shows a block diagram of a preferred system of the invention, and

Fig. 2 illustrates a circuit diagram, having some block ICC Referring now to the drawings, there is shown in Fig.

1 (which illustrates a preferred system) a power supply i 11 for providing electrical energy to modulator 12 and magnetron 13. Modulator 12 controls magnetron 13 which transmits radio frequencyl energy into space by means of antenna system 15. The cathode current of magnetron 13 is amplified by current amplifier 16 and is fed to modulator 12 to provide degenerative feedback to cancel changes in the radio frequency output of magnetron 13. i i Y One of the many possible embodiments of the system of Fig. l is illustrated in Fig. 2. Three-phase energy is fed by a source (not shown) to a frequency-phase converter 17 which converts this energy into single-phase energy having a frequency three times that of the threephase energy. This single-phase energy passes through charging inductor 19 to charging capacitor 20. A first stage saturable-core discharge reactor 21 having control winding 23 is joined between one terminal of capacitor 26 and a tap on autotransformer 24. A conventional pulse-forming network 25 is connected across autotransformer 24 and feeds pulses into a second stage saturating reactor 27 which is connected to a terminal on autotransformer 28. The pulses from autotransformer 20 are coupled via capacitors 29 and 31 across bifilar inductor 32 to the cathode of magnetron 13.. Electrical energy for the filament of magnetron 13 is obtained by transformer 34 in the customary fashion. Lead 35 conducts the cathode current of magnetron 13 to windings 36 and 33 of magnetic amplifier 16. A reference cur rent, w'hose magnitude is controlled by rheostat 41, is supplied to windings 42 and 43 from source 46. Windings 47 and 48 each have a terminal connected to one phase of the afore-mentioned three-phase source and the other terminals of these windings are joined, respectively, through oppositely poled rectifiers 5f) and 51 to full-wave rectifier 52. The output of rectifier 52 is smoothed by low-pass filter 54 and is then conducted to the control winding 23 of saturable-core reactor 21. Since magnetron 13 is essentially a constant voltage device, any change in its radio frequency output must be accompanied by a change in cathode current. This change in cathode current is amplified by magnetic :amplifier 16 and is filtered by filter 54 and applied to the control winding 23 of saturable-core reactor 21 where it acts as a bias to control the output of modulator 12 which in turn alters the output of magnetron 12 to cancel the initiating radio frequency power change.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

l. A system for maintaining an essentially constant radio frequency output from a circuit comprising a magnetron which is controlled by a modulator 'that employs several stages of saturable-core reactors as discharge elements, said system comprising: means for amplifying the cathode current of said magnetron, means for converting said amplified cathode current into a smooth D.C. current, and means for applying the smooth D C. current to a control winding of one of the saturable-core reactors in said modulator whereby the output of said modulator is controlled so that the magnetron radio frequency output is maintained essentially constant.

2. In a radar system having a magnetron output device and saturable-core reactor stages for the production of magnetron input pulses, a magnetron output regulating circuit comprising: means for amplifying the cathode current of the magnetron, and means for utilizing the amplified cathode current for controlling the bias of at least one of the saturable-core reactors in said saturablecore reactor stages whereby an essentially constant radio frequency'output is obtained from said magnetron.

3.- Ina radar system having a magnetron output tube and Va modulator comprising at least one saturablecore reactor stage, a magnetron output regulating circuit comprising: magnetic amplifier means for amplifying the cathode current of the magnetron, rectifier means for full-wave rectifying the output from said netic amplifier means, filter means for filtering the output of said rectifier means, and conductor means for applying the output of said filter means to the saturable-core reactor stage in the modulator whereby an essentially constant radio frequency output isobtained from said magnetron.

4. A radar system comprising a magnetron output tube, a modulator including a pulse forming network coupled to the cathode of said magnetron and a current responsive impedance, circuit means coupling said pulse forming network through said current responsive iinpedance to a pulse source, means for measuring amplifying the cathode current of said magnetron, and circuit means coupling the output from said last mentioned means to said current responsive impedance whereby an essentially constant radio frequency output is obtained from said magnetron.

5. The radar system of claim 4 wherein said current responsive impedance comprises a saturable core reactor including a load winding connected between said pulse source and said pulse forming network and further including a bias winding coupled to receive the output from said cathode current measuring and amplifying means;

6. The radar system of claim 5 wherein said cathode current measuring and amplifying means comprises a magnetic amplifier having the control windings thereof connected in series with the cathode of said magnetron, a full wave rectifier, circuit means coupling the input terminals of said full rectifier to an alternating voltage source through the load windings of said magnetic amplifier, a low pass filter, and circuit means coupling the output terminals of said rectifier through said low pass filter to the bias winding of said saturable core reactor.

7. A control circuit for maintaining an essentially constant radio frequency output from a magnetron, said circuit comprising a modulator for controiling the operation of the magnetron, means for amplifying the cathode current of said magnetron, means for applying the amplified cathode current to bias said modulator in a manner such that an essentially constant radio frequency output is obtained from said magnetron, and a bias sensitive element in said modulator comprising a saturable'- core reactor with a control winding.

8. The system of claim 7 wherein said means for amplifying the cathode current is a magnetic amplifier.

References Cited in the file of this patent UNITED STATES PATENTS 2,440,320 Young Apr. 27, 1948 2,659,866 Landon Nov. 17, 1953 2,673,296 Crapuchettes Mar. 23, 1954. 2,694,149 Gross Nov, 9, 1954 2,790,948 Wennerberg Apr. 30, 1957 OTHER REFERENCES Feedback Control System, McGraw, Hill, by Burns and Saunders, published 1955 (chapter 8). 

